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Antarctic Ice Shelf Suffers Loss

A chunk of ice twice the size of Manhattan broke away from the northernmost part of the Antarctic peninsula in February, and scientists are blaming rising temperatures. The stability of such ice shelves in both polar regions is an important factor for climate models designed to predict the effects of a rise in global temperatures.

Satellite images analyzed by glaciologist Ted Scambos and his colleagues at the National Snow and Ice Data Center in Boulder, Colorado, show that the ice broke off from the Larsen B ice shelf, a 300-meter-thick sheet roughly the size of Connecticut. This loss, representing 5% of the ice shelf, is consistent with a prediction made earlier this year by glaciologist Christopher Doake's group at the British Antarctic Survey in Cambridge that the ice shelf is unstable and that a significant portion would break off before the end of the decade. "It's a nice juxtaposition of observation and theory," says Scambos. The analysis came in a press release of work that has not yet been submitted for publication.

The Larsen ice shelf is believed to have formed as long ago as the last Ice Age, when a bay failed to thaw in the summer and ice and snow flowed down from mountain glaciers into the bay. Over time, the thickening ice merged into a uniform plate. Since the 1940s, however, air temperatures in the Antarctic Peninsula have risen on average 2.5 degrees Celsius, melting ice on the shelf's surface. This surface melting, coupled with slight increases in ocean temperature, has allowed cracks to spread through the shelf. "Ice is a fairly soft material--fractures can propagate through it in the warm season ... sort of like a piece of broken auto glass," says Scambos.

Scambos says the relatively rapid changes in the Larsen ice shelf make it "a fairly unambiguous marker of climate change." That's also how it looks to Christina Hulbe, a geologist at the University of Chicago, who sees the February event as a sign of things to come. "With the warming we've observed, there's going to be big changes in these ice shelves," she says.